|Mission type||Crewed lunar orbital CSM/LM flight (F)|
|Mission duration||8 days, 3 minutes, 23 seconds|
|Launch mass||98,273 pounds (44,576 kg)|
|Landing mass||10,901 pounds (4,945 kg)|
|Start of mission|
|Launch date||May 18, 1969, 16:49:00UTC|
|Rocket||Saturn V SA-505|
|Launch site||Kennedy LC-39B|
|End of mission|
|Recovered by||USS Princeton|
|Landing date||May 26, 1969, 16:52:23UTC|
|Periselene altitude||109.6 kilometers (59.2 nmi)|
|Aposelene altitude||113.0 kilometers (61.0 nmi)|
|Spacecraft component||Command and service module|
|Orbital insertion||May 21, 1969, 20:44:54 UTC|
|Orbital departure||May 24, 1969, 10:25:38 UTC|
|Spacecraft component||Lunar module|
|Periselene altitude||14.4 kilometers (7.8 nmi)|
|Docking with LM|
|Docking date||May 18, 1969, 20:06:36 UTC|
|Undocking date||May 22, 1969, 19:00:57 UTC|
|Docking with LM Ascent Stage|
|Docking date||May 23, 1969, 03:11:02 UTC|
|Undocking date||May 23, 1969, 05:13:36 UTC|
Left to right: Cernan, Stafford, Young
Apollo 10 (May 18 – 26, 1969) was a human spaceflight, the fourth crewed mission in the United States Apollo program, and the second (after Apollo 8) to orbit the Moon. It was the F mission: a "dress rehearsal" for the first Moon landing, testing all the components and procedures just short of actually landing. While astronaut John Young remained in the Command Module orbiting the Moon, astronauts Thomas Stafford and Gene Cernan flew the Apollo Lunar Module (LM) to a descent orbit within 8.4 nautical miles (15.6 km) of the lunar surface, the point where powered descent for landing would begin. After orbiting the Moon 31 times, Apollo 10 returned safely to Earth, and its success enabled the first actual landing (Apollo 11) two months later.
Apollo 10 set the record for the highest speed attained by a crewed vehicle: 39,897 km/h (11.08 km/s or 24,791 mph) on May 26, 1969, during the return from the Moon.
The mission's call signs were the names of the Peanuts characters Charlie Brown and Snoopy, who became Apollo 10's semi-official mascots. Peanuts creator Charles Schulz also drew mission-related artwork for NASA.
|Commander||Thomas P. Stafford|
|Command Module Pilot||John W. Young|
|Lunar Module Pilot||Eugene A. Cernan|
|Commander||L. Gordon Cooper Jr.|
|Command Module Pilot||Donn F. Eisele|
|Lunar Module Pilot||Edgar D. Mitchell|
Apollo 10 and Apollo 11 were the only Apollo missions whose crew were all veterans of spaceflight. Thomas P. Stafford had flown on Gemini 6 and Gemini 9; John W. Young had flown on Gemini 3 and Gemini 10, and Eugene A. Cernan had flown with Stafford on Gemini 9.
In addition, Apollo 10 was the only Saturn V flight from Launch Complex 39B, as preparations for Apollo 11 at LC-39A had begun in March almost immediately after Apollo 9's launch.
They were also the only Apollo crew all of whose members went on to fly subsequent missions aboard Apollo spacecraft: Young later commanded Apollo 16, Cernan commanded Apollo 17 and Stafford commanded the U.S. vehicle on the Apollo–Soyuz Test Project. It was on Apollo 10 that John Young became the first human to fly solo around the Moon, while Stafford and Cernan flew the LM in lunar orbit as part of the preparations for Apollo 11. Young was also backup commander of Apollo 13 and Apollo 17 and Cernan was backup commander of Apollo 14.
The Apollo 10 crew are the humans who have traveled the farthest away from their (Houston) homes, at a distance of 408,950 kilometers (220,820 nmi) (though the Apollo 13 crew was 200 km farther away from Earth as a whole). While most Apollo missions orbited the Moon at the same 111 kilometers (60 nmi) from the lunar surface, the distance between the Earth and Moon varies by about 43,000 kilometers (23,000 nmi), between perigee and apogee, throughout each lunar month, and the Earth's rotation makes the distance to Houston vary by at most another 11,000 kilometers (5,900 nmi) each day. The Apollo 10 crew reached the farthest point in their orbit around the far side of the Moon at about the same time Earth's rotation put Houston nearly a full Earth diameter farther away.
By the normal rotation in place during Apollo, the backup crew would have been scheduled to fly on Apollo 13.[note 1] However, Alan Shepard, then number two at the Astronaut Office, gave himself the Apollo 13 command slot instead. L. Gordon Cooper Jr., Commander of the Apollo 10 backup crew, was enraged and resigned from NASA. Deke Slayton, the Director of the Flight Crew Operations also removed Donn F. Eisele from the crew due to the personal misconduct and a professional misconduct in the Apollo 7 mission and was replaced by Stuart Roosa. Later, Shepard's crew was forced to switch places with Jim Lovell's tentative Apollo 14 crew.
Slayton wrote in his memoirs that Cooper and Eisele were never intended to rotate to another mission as both were out of favor with NASA management for various reasons (Cooper for his lax attitude towards training, and Eisele for incidents aboard Apollo 7 plus an extramarital affair) and were assigned to the backup crew simply because of a lack of qualified manpower in the Astronaut Office at the time the assignment needed to be made. Cooper, Slayton noted, had a very small chance of receiving the Apollo 13 command if he did an outstanding job with the assignment, which he did not. Eisele, despite his issues with management, was always intended for future assignment to the Apollo Applications Program (which was eventually cut down to only the Skylab component) and not a lunar mission.
|Component||Apollo 10 LM-4||Apollo 11 LM-5|
|Desc. stg. dry||4,703||2,133||4,483||2,033|
|Desc. stg. propellant||18,219||8,264||18,184||8,248|
|Desc. stg. subtotal||22,922||10,397||22,667||10,282|
|Asc. stg. dry||4,781||2,169||4,804||2,179|
|Asc. stg. propellant||2,631||1,193||5,238||2,376|
|Asc. stg. subtotal||7,412||3,362||10,042||4,555|
This dress rehearsal for a Moon landing brought the Apollo Lunar Module to 8.4 nautical miles (15.6 km) from the lunar surface, at the point where powered descent would begin on the actual landing. Practicing this approach orbit would refine knowledge of the lunar gravitational field needed to calibrate the powered descent guidance system to within 1 nautical mile (1.9 km) needed for a landing. Earth-based observations, uncrewed spacecraft, and Apollo 8 had respectively allowed calibration to within 200 nautical miles (370 km), 20 nautical miles (37 km), and 5 nautical miles (9.3 km). Except for this final stretch, the mission was designed to duplicate how a landing would have gone, both in space and for ground control, putting NASA's flight controllers and extensive tracking and control network through a rehearsal.
The ascent stage was loaded with the amount of fuel and oxidizer it would have had remaining if it had lifted off from the surface and reached the altitude at which the Apollo 10 ascent stage fired; this was only about half the total amount required for lift off and rendezvous with the CSM. The mission-loaded LM weighed 30,735 pounds (13,941 kg), compared to 33,278 pounds (15,095 kg) for the Apollo 11 LM which made the first landing. Craig Nelson wrote in his book Rocket Men that NASA took special precaution to ensure Stafford and Cernan would not attempt to make the first landing. Nelson quoted Cernan as saying "A lot of people thought about the kind of people we were: 'Don't give those guys an opportunity to land, 'cause they might!' So the ascent module, the part we lifted off the lunar surface with, was short-fueled. The fuel tanks weren't full. So had we literally tried to land on the Moon, we couldn't have gotten off."
On May 22, 1969, at 20:35:02 UTC, a 27.4 second LM descent propulsion system burn inserted the LM into a descent orbit of 60.9 by 8.5 nautical miles (112.8 by 15.7 km) so that the resulting lowest point in the orbit occurred about 15° from lunar landing site 2 (the Apollo 11 landing site). The lowest measured point in the trajectory was 47,400 feet (14.4 km) above the lunar surface at 21:29:43 UTC.
Shortly after trans-lunar injection, Young performed the transposition, docking, and extraction maneuver, separating the command and service module (CSM) from the S-IVB stage, turning around, and docking its nose to the top of the lunar module (LM), before separating from the S-IVB. Apollo 10 was the first mission to carry a color television camera inside the spacecraft, and made the first live color TV transmissions from space.
After reaching lunar orbit three days later, Young remained in the command module (CM) Charlie Brown while Stafford and Cernan entered the LM Snoopy and flew it separately. The LM crew performed the descent orbit insertion maneuver by firing their descent engine, and tested their craft's landing radar as they approached the 50,000-foot (15,000-meter) altitude where the subsequent Apollo 11 mission would begin powered descent to actually land on the Moon. They surveyed the future Apollo 11 landing site in the Sea of Tranquility, then jettisoned the descent stage and fired the engine of the ascent stage to return to Charlie Brown Command Module. The descent stage was left in orbit, but eventually may have crashed onto the lunar surface because of the Moon's non-uniform gravitational field. Its location is unknown as it was not tracked.
During descent stage separation, the lunar module began to roll unexpectedly because the crew accidentally duplicated commands into the flight computer which took the LM out of abort mode, the correct configuration for this maneuver. The live network broadcasts caught Cernan and Stafford uttering several expletives before regaining control of the LM. Decades later, Cernan said he observed the horizon spinning eight times over, indicating eight rolls of the spacecraft under ascent engine power. Recordings from the flight do not support this dramatic memory. While the incident was downplayed by NASA, the roll was just several revolutions from being unrecoverable, which would have resulted in the LM crashing into the lunar surface.
After Stafford and Cernan docked with and re-entered Charlie Brown, Snoopy's engine was fired to fuel depletion to send the ascent stage on a trajectory past the Moon and into a heliocentric orbit. This maneuver was unlike the fate of the subsequent Apollo 11 ascent stage, which was left in lunar orbit to eventually crash (post-Apollo 11 ascent stages were steered into the Moon to obtain readings from seismometers placed on the surface, except for Apollo 13's ascent stage, which the crew used as a "life boat" to get safely back to Earth before releasing it to burn up in Earth's atmosphere).
Snoopy's ascent stage orbit was not tracked after 1969, and its current location is unknown. In 2011, a group of amateur astronomers in the UK started a project to search for it. In 2019, the Royal Astronomical Society announced a possible rediscovery of Snoopy, determining that small Earth-crossing asteroid 2018 AV2 is likely the capsule with "98%" certainty. It is the only once-crewed spacecraft still in outer space without a crew.
Splashdown occurred in the Pacific Ocean on May 26, 1969, at 16:52:23 UTC, about 400 nautical miles (740 km) east of American Samoa. The astronauts were recovered by USS Princeton, and subsequently flown to Pago Pago International Airport in Tafuna for a greeting reception, before being flown on a C-141 cargo plane to Honolulu.
After Apollo 10, NASA required astronauts to choose more "dignified" names for their command and lunar modules. This proved unenforceable: Apollo 16 astronauts Young, Mattingly and Duke chose Casper, as in Casper the Friendly Ghost, for their command module name. The idea was to give children a way to identify with the mission by using humor.
The Smithsonian has been accountable for the command module Charlie Brown since 1970. The spacecraft was on display in several countries until it was placed on loan to the London Science Museum in 1978. Charlie Brown's service module (SM) was jettisoned just before re-entry and burned up in the Earth's atmosphere.
After translunar injection, the Saturn V's S-IVB third stage was accelerated past Earth escape velocity and became a derelict object where as of 2020[update], it remains in a heliocentric orbit.
The ascent stage of the Apollo Lunar Module Snoopy was jettisoned into a heliocentric orbit. On June 10, 2019, Nick Howes, a fellow of the Royal Astronomical Society, announced that he and his colleagues had located Snoopy, whose location was previously unknown, based on radar astronomy data with 98% certainty.
Snoopy's descent stage was jettisoned in lunar orbit; its current location is unknown. Further, it is unclear whether the descent stage impacted the lunar surface, or if it remains in lunar orbit. Phil Stooke, a planetary scientist who studied the lunar crash sites of the LM's ascent stages, wrote that the descent stage "crashed at an unknown location", and another source stated that the descent stage "eventually impact(ed) within a few degrees of the equator on the near side". However, Richard Orloff and an official NASA mission summary stated simply that the descent stage entered lunar orbit, remaining silent on the question of whether the stage later impacted the Moon. An amateur astronomy blog begun in early 2020 explored the possibility that the descent stage may still be in lunar orbit, using computer simulation.
The shield-shaped emblem for the flight shows a large, three-dimensional Roman numeral X sitting on the Moon's surface, in Stafford's words, "to show that we had left our mark". Although it did not land on the Moon, the prominence of the number represents the significant contributions the mission made to the Apollo program. A CSM circles the Moon as an LM ascent stage flies up from its low pass over the lunar surface with its engine firing. The Earth is visible in the background. On the mission patch, a wide, light blue border carries the word APOLLO at the top and the crew names around the bottom. The patch is trimmed in gold. The insignia was designed by Allen Stevens of Rockwell International.
In February 2016 Discovery Channel broadcast a TV show suggesting that the mission witnessed mysterious or alien signals while on the far side of the Moon. The astronauts mention the odd whistling sound that lasted nearly an hour. It was speculated that this is evidence for UFO coverup. According to space journalist James Oberg, the sound was most probably radio interference between the command module and the lunar module landing vehicles. Describing it as "outer-space type music" was most probably due to priming, as suggested by Benjamin Radford.